Accept Google Application Default Credentials (authorized_user) in the
Vertex apiKey field as an alternative to Service Account JSON, for orgs
that block SA key creation. Refreshes a Bearer token via the existing
refreshGoogleToken flow and requires a project_id (quota_project_id or
providerSpecificData.projectId). SA JSON and raw key flows unchanged.
Co-authored-by: Cursor <cursoragent@cursor.com>